1. Field of The Invention
This invention relates to a process for the recovery of precious metals from carbonaceous ores and mixtures of carbonaceous and oxide ores containing such metals by leaching and electrodeposition techniques.
2. Prior Art
Present practices in the field of gold and silver recovery from ores often require segregation of such ores prior to their processing, of which ores there are two basic types: first, oxide ores from which precious metal values are easily extracted by present cyanidation techniques, and second, carbonaceous ores which are refractory to conventional cyanidation techniques and which are characterized by their organic carbon content, which is normally between 0.25 and 3% by weight. To render the latter more amenable to cyanide extraction a single- or multi-stage pretreatment prior to cyanidation is normally required to prevent the carbonaceous component of the ore from adsorbing the gold- or silver-cyanide complex formed during leaching. This pretreatment alone can consume up to approximately thirty hours of processing time and necessitates costly plant equipment and operating expenditures. When more than one type of ore have to be treated the types must be segregated prior to treatment and treated by different techniques. These techniques are usually time consuming and necessitate costly plant equipment and operating expenditures.
Various patents have separately addressed the use of electrodeposition to recover precious metals from oxide and similar type of ores. Thus, for example, U.S. Pat. No. 836,380 (Hendryx) teaches the recovery of gold and silver from oxide-type gold-ferrous ores and oxide-type silver-ferrous ores by forming a pulp of cyanide and ore which is crushed, amalgamated and ground. Suitable chemicals are then added to eliminate certain deleterious acid salts and the pulp is allowed to settle, after which the cyanide level is built back up and the pulp is subjected to an electrical current of seven to ten volts to electrodeposit the metal values. The patent does not disclose the addition of a base to maintain an alkaline pH or the simultaneous leaching and electrodeposition process of this invention.
U.S. Pat. No. 668,842 (Rouse) discloses an apparatus for the extraction of gold and silver from their ores by electrolytically treating the ore pulp. The pulp is placed in a vessel, the desired reagents are added and an electrical potential of 5 to 10 volts is then applied. The cathodes are made of gold and silver from previously used cathodes, and the gold and silver precipitate thereon. Rouse's patent does not address the processing of carbonaceous ores or mixtures of carbonaceous and oxide ores, nor does it disclose the conditions for providing the partial dissolution of the precious metal values needed to conduct the simultaneous leaching and electrodeposition of this invention.
U.S. Pat. No. 893,472 (Forget) discloses another apparatus for recovering gold from slimes and gold-bearing ores in a weak cyanide solution with an electric current, but fails to disclose the conditions necessary to provide for the partial dissolution of the precious metal values needed to conduct the simultaneous leaching and electrodeposition of this invention.
U.S. Pat. No. 978,211 (Robertson) discloses injecting powdered ore into an electrolyte in a tank. When the ore contains gold, the electrolyte can be potassium cyanide. The electrolyte is agitated by steam or hot air while subjected to an electrical current. The process of simultaneous leaching and electrodeposition, as described in the present invention, does not appear in said patent.
U.S. Pat. Nos. 61,866 (Rae I) and 62,776 (Rae II) teach treating pulverized gold- or silver-bearing ore in potassium cyanide solution with agitation and electrical current but fail to disclose the conditions for providing the partial dissolution of the precious metal values needed to conduct the simultaneous leaching and electrodeposition of this invention.